This project is designed to examine the interrelationships among frequency selectivity, nonlinearities and speech perception in a group of normal listeners and three groups of hearing-impaired listeners (a) Patients with a precipitious SensoriNeural Hearing Loss (SNHL) limited to frequencies above 1500 Hz. (b) patients with a unilateral sudden-onset SNHL, (c) patients with a long-term flat SNHL. Measures of Psychophysical Tuning Curves, Lateral Suppression, Combination Tone generation and performance on the CUNY Nonsense Syllable Test (NST) will be obtained from all Ss via an adaptive procedure. The goal of the investigation is to examine 1) the interactions among these measures in the same listeners and 2) the extent to which sensitivity, frequency selectivity and nonlinear characteristics account for the difficulty to understand speech in noise encountered by normal and, in particular, hearing-impaired listeners. The hope is that the results will lead to refined differential diagnosis of auditory pathologies and the development of more effective amplification systems and rehabilitation methods.